1. Field of the Invention
The invention relates to the field of electric hand tools, in particular to a method of driving a reciprocating sander in combination with an extension arm.
2. Description of the Prior Art
Much of the sanding of cabinet and finish work is done with electric sanders. Presently, electric sanders are of three general designs, namely a linear reciprocating sander, a rotary disc sander, or an orbital sander. Each design has its own advantages with respect to performance, reliability, cost of construction and ease of use. Disc and orbital sanders are characterized, of course, by a rotary motion of the sanding disc. Such sanding discs are necessarily circular in order to accommodate the rotary motion of the sander. However, much of the cabinet and finished work requires the ability to sand in the corners into which the circular disc cannot be placed. For this reason, belt or reciprocating sanders having a generally rectangular sanding surface are particularly useful. However, the performance of belt or reciprocating sanders as known in the prior art, particularly in tight corners, still leaves an area on the margin of the corner which can not be reached by the sander. Clearly, this area includes a width equal to the radius of the rotor on a belt sander and, in the case of a reciprocating sander, may include a distance equal to the overhang of the sander body beyond the limit of vibration of the sanding surface. In addition regardless of the motive apparatus for moving the sandpaper, when the sandpaper is wrapped around the ends of the sanding pad, a small curvature along at least two opposing edges of the sanding surface is unavoidably formed. Such a curvature serves to limit the effective distance to an adjacent edge or wall within which such a sander can operate. For the purposes of this specification areas in such corners which cannot be reached due to sander configuration or design shall be defined as "dead zones."
Furthermore, even in the case where the dead zone is relatively small, the design of such reciprocating sanders requires the motive source for reciprocation to be mounted immediately behind the sanding pad. Normally, such a vibrating motor operates at relatively high frequencies and with small excursions. The vibrating motion is imparted by such motors to the sanding pad in such a way that close and intimate contact is needed between the vibrator and the sanding pad. Therefore, when such sanders must be used to sand relatively inaccessible surfaces, such as ceilings and corners of ceilings and walls, the great bulk of the tool's weight must be carried by the user above his head and often at extended distances from the body. This type of usage quickly results in fatigue and pose a serious practical limitation on the degree to which such tools can be effectively be used to sand ceilings, upper walls and other relatively inaccessible surfaces.
What is needed then is a sander which is characterized by having virtually no dead zone and which is of such a design as to permit usage on relatively inaccessible surfaces such as ceilings or upper walls in such a manner that prolonged use by the user does not cause fatigue or requires strength and strenuous effort to hold the tool in place or to manipulate it for extended times.